What Are Shaders?
Shaders define the look of visuals in Minecraft, and lots of other programs.
For the purpose of this book, Shaders won't be covered in detail, but you can check out the Minecraft Wiki's article for a more in-depth overview: minecraft.wiki/w/Shader
Is my hardware able to render custom Shaders?
Some shader packs aren't complex enough to require very modern hardware. However, in general it's recommended to have an RTX 30 series GPU or newer, and a somewhat recent mid-range or better CPU (Anything within the last 6 years is likely good enough). An extra couple GBs of RAM allocated to the game are also recommended.
How do I use custom Shaders?
To enable Shaders, you need a Mod.
For the Fabric and NeoForge Modloader, Iris is your best friend. Alongside Iris, on Fabric you need Sodium, on NeoForge you'll want to use Embeddium alongside Monocle.
To add Shaders, launch the game with the mods above, then head to Options > Video Settings > Shader Packs, then add and enable your Shaders there.
If you somehow stumbled upon Optifine for Shader support, please do not use it, for reasons explained here: OptiFine